The invention relates to a strong shaking judgment device and method, and more particularly to a device and method used to judge a strong shaking using judgment logic.
Earthquakes cannot be predicted and they cause tremendous casualties and property loss. The big earthquake that happened in Taiwan on Sep. 21, 1999 is a distinct example. In this disaster, there were many causes of casualties and losses, such as buildings collapsing, gas explosions or fire caused by the rupture of electrical wires, or property loss caused by precision instruments being disabled. In order to avoid such casualties and losses, the architectural design of buildings must focus on increasing strength, and other factors such as gas and electrical facilities can be provided with an earthquake warning device and switched-off through a proper method. Therefore, how to build a dependable strong shaking judgment method, applicable to microcomputer gas meters, mass transit systems, precision instruments, etc., that can emit a strong shaking warning signal and shut down the power supply of facilities to avoid greater casualties in order to lessen the losses of personnel and properties when a strong shaking happens is an important research today.
A seismic sensor applied on a gas meter is disclosed in U.S. Pat. No. 5,408,457. The method that this patent reveals is to hang a steel ball in a space. The displacement of the steel ball causes its upper circuit to yield an On-Off signal when a shaking happens. This signal can be used to represent the occurrence of a shaking. The greatest benefit of this method is that its structure is simple and little electricity is consumed (almost without consumption of electricity). However, the biggest shortcoming is that it cannot measure the strength of an earthquake accurately. Therefore, judgment logic must be used in coordination with such a method to judge the occurrence of the earthquake accurately. In addition, it is easy to misjudge because the shaking comes from the outside, piping is too long and the device is disposed in a tall building.
Another research in Taiwan proposes an earthquake judgment logic device utilizing a steel ball type seismic sensor. Its earthquake judgment mainly rests on taking a total time length of earthquake signals, shaking period numbers and the time length of each period as characteristic values of earthquake judgment to form a judgment logic table. The greatest benefit of this method is that a microcomputer controlled circuit saves a lot of work after the table of the judgment logic is constructed. However, it also has the shortcoming of the steel ball type switch mentioned above. Besides, this kind of judgment logic is not necessarily suitable for use everywhere because earthquake modes at different places are not exactly the same.
It can be known from the earthquake characteristics proposed by Douglas P. Arduini in his paper xe2x80x9cSmart sensor requirements for second generation seismic gas shut-off valvesxe2x80x9d that a vertical shaking wave (p-wave) has faster wave transmission speed than a horizontal wave (s-wave) when an earthquake occurs. Moreover, the shaking strength and destructiveness of a p-wave is also far smaller than that of an s-wave. Therefore, the micro type shaking switch designed in the semiconductor manufacturing process for exploring the earthquake wave in the vertical direction disclosed in U.S. Pat. No. 5,742,235 is used to avoid earthquake casualties. The benefits of this patent are that it is very simple in structure and the elements are cheap. But, in fact, according to earthquake strength data the strength of p-waves in general is very small (approximately 0.01 g). Therefore, misjudgment is easy if earthquake judgment only rests on earthquake sensing in a single perpendicular direction. Therefore, it is proper that other earthquake judgment methods are included.
A fluid type seismic sensor disclosed in U.S. Pat. No. 4,165,503 can be used to measure a shaking and linear acceleration. Sensing mass and sensing fluid are used to act together on a pressure transformer to yield a telecommunication output equal to G value. The design of this sensor can be suitable for use in a broad G value range; it is limited to the maximum value on the reading table. The biggest difference between this design and the traditional design is the method that action transforms into pressure output. Net pressure yielded from the fluid and sensed by the sensing mass can be read through the pressure transformer. It is directly proportional to acceleration load.
A multifunctional earthquake transformer is disclosed in U.S. Pat. No. 4,253,164. The response characteristics and transfer function of its output signal can be changed arbitrarily in order to duplicate a transfer function needed for another seismic sensor. This change can be processed at a measurement site. The invention provides a transfer function shaping filter. The central frequency of the shaping filter can be adjusted to the natural frequency of the seismic sensor. The parameters of the filter can be designed to be adjustable in order to be in coordination with the damping effect and phase response of the seismic sensor. The transfer function of the invention comprises a first transfer function of a first sensor (accelerometer or hydrophone) in order to be in coordination with a second transfer function of a second sensor (geophone).
A seismic sensor for intrusion detection disclosed in U.S. Pat. No. 4,333,029 includes a base, a cantilever member of piezoelectric construction extending from the base, and a mass loading the end of the cantilever member separate from the base. The base defines a slot for receiving the end of the cantilever member, and holes, perpendicular to the slot, for receiving electrical conductors. These conductors are configured to orient the cantilever member at 45 degrees relative to the horizontal plane, providing sensing in both the X direction and the Y direction. A housing encloses the sensor, and another leg extends from the housing at the end separate from the base, enhancing the mechanical coupling between the sensor and the surface on which it is supported.
A seismic sensor disclosed in U.S. Pat. No. 4,361,740 essentially consists of a central annular member having an inner conductive periphery. The annular member is coaxially positioned around a center post located in a housing. The center post has four extending surface slots into which are inserted tines or upstanding flanges associated with first and second contact members. The contact members enable the sensor to be mounted in four distinct positions.
A method disclosed in U.S. Pat. No. 5,823,223 is to place a blocking trip ball on a small tray. When an earthquake is beyond the preset allowable range, the trip ball slides out from the small tray and drops into a piping to block the pipe. It not only is simple in structure, but also the shape and size of the small tray can be adjusted if necessary.
An inclined sensor disclosed in U.S. Pat. No. 4,972,595 is a single shaft sensor. It is mainly used to alleviate the problem that the volume is too large for a traditional inclined sensor in order to be disposed in a car. The traditional inclined sensor is a long horizontal shaft, and it must have a definite length in order to increase sensitivity. A valley type groove is designed in the invention, and a circle is placed at the bottom of the valley. The circle climbs upward along a slope, and a sensor on the slope senses the inclined angle when inclination occurs. This sensor can be inlayed in a circuit board of a car.
An earthquake emergency shut-off valve is disclosed in U.S. Pat. No. 4,382,449. It mainly installs a movable magnet outside a pipe. The magnet is used to drive a steel ball inside the piping; its front end leans against a spring switch. The magnet falls off the spring switch to lead the steel ball inside the pipe to shut off the valve.
The patents relating to earthquake judgment and blocking technology mentioned above all cannot consider on every possible situation of an earthquake judgement. For instance, if a detected shaking is emitted from a drilling machine, in fact, it is noise; or the effect of a small earthquake on the upper levels of a building and on the lower levels of a building is different. Besides, as to earthquake judgment logic, the above-mentioned technology use an acceleration parameter yielded from earthquake to judge an earthquake, an overall consideration to different attributes isn""t done as well. That is to say, how to develop an earthquake judgment method that can consider the height factors of different building layers and noise generation in order to avoid misjudgment caused from outside interference (vibration frequencies of a earthquake are at 0-20 Hz), factor in influences caused by earthquakes of different energy levels, and judge immediately and shut off gas and electricity facilities is an important research topic.
The object of the invention is to provide a strong shaking judgment method used to analyze earth acceleration waveform change and judge a strong shaking.
Another object of the invention is to provide a strong shaking judgment method and device used to improve the traditional On-Off type seismic sensor and the shortcomings of misjudgment caused by the traditional strong shaking judgment method.
Another object of the invention is to provide a strong shaking judgment method and device that factors in the influence of magnification effects of building height on acceleration, velocity and displacement to be removed by using modification parameters to tall buildings. Especially in low frequency earthquakes, the acceleration on the earth""s surface is 0.2 g; it is probably 0.6 g at the 12th building layer.
Accordingly, the invention provides a strong shaking judgment method enabling data of an acceleration threshold, energy index upper limit, middle limit and lower limit to be calculated according to data of maximum acceleration and shaking energy index obtained at a seismic event. Thus, when a shaking occurs the device and method of the invention can determine whether it is an earthquake by using the above-mentioned data. The method comprises the following steps: sample the acceleration of the shaking to obtain a maximum acceleration, calculate the energy of the shaking to obtain energy value, compare the maximum acceleration with an acceleration threshold and both energy value and energy index to obtain a strong shaking judgment index. Thereafter, a strong shaking can be judged according to the strong shaking judgment index.
The strong shaking judgment index can be obtained according to the following judgment rules: the strong shaking judgment index is assigned to the occurrence of a strong shaking when the measured maximum acceleration is greater than the upper limit of the acceleration threshold and the energy value is greater than the lower limit of the energy index lower limit. On the other hand, the strong shaking judgment index is assigned to non-occurrence of a strong shaking if the energy value is smaller than the energy lower limit.
The strong shaking judgment index is assigned to the occurrence of a strong shaking when the measured maximum acceleration is smaller than the upper limit of the acceleration threshold but greater than the middle limit, and the energy value is greater than the middle limit of the energy index. But, a first conditional earthquake judgment is processed if the energy value is smaller than the middle limit of the energy index but greater than the lower limit. The strong shaking judgment index is assigned to the non-occurrence of a strong shaking if the energy value is not only smaller than the middle limit of the energy index, but also smaller than the lower limit.
The strong shaking judgment index is assigned to the occurrence of a strong shaking when the maximum acceleration is smaller than the middle limit of the acceleration threshold and the energy value is greater than the upper limit of the energy index. But, a second conditional earthquake judgment is processed if the energy value is smaller than the upper limit of the energy index but greater than the middle limit. A third conditional earthquake judgment is processed if the energy value is smaller than the middle limit of the energy but greater than the lower limit. The strong shaking judgment index is assigned to non-occurrence of a strong shaking if the energy value is not only smaller than the middle limit of the energy index but also smaller than the lower limit of it.
The conditional earthquake judgments mentioned above can set a safe zone judgment. For example, increase a specified proportion of the maximum safe displacement or the maximum safe velocity as a judgment value, such as 60 percent. Being not in the safe zone is judged if this specified judgment value is exceeded, i.e. a strong shaking happens.
Besides, other judgment rules can be added, for example including a low-pass filtering step. The strong shaking judgment is stopped if the shaking frequency is greater than the low-pass filtering frequency, but the comparison steps are processed only if the shaking frequency is smaller than the low-pass frequency filtering frequency.
Additionally, the invention can use the maximum velocity and the maximum displacement indexes to judge the occurrence of a strong shaking, and these two indexes can be calculated through acceleration values. Therefore, the following judgment steps can be added: the strong shaking judgment index is assigned to the occurrence of a strong shaking if the maximum displacement is greater than the maximum safe distance. Comparisons are processed between the maximum acceleration value and the acceleration threshold, and between the energy value and the energy index if the maximum velocity is smaller than the maximum safe velocity and the maximum displacement is smaller than the maximum safe displacement.
Meanwhile, for putting the above-mentioned method into practice, the invention also provides a strong shaking judgment device. It is made according to the strong shaking judgement method which comprises: a battery module used to provide electricity for the device, an acceleration sensor module used to sense shaking acceleration value and calculate an energy value, a micro controller module which comprises an earthquake sensing program used to receive the acceleration values mentioned above and compare the maximum acceleration threshold value with the acceleration value and the shaking energy index with the energy value, an alarm output module used to receive a warning signal and to send out an alarm, and a state display module used to receive a state signal and to display the state of the device.